Controlled Rate Thermal Analysis Research Articles

The thermal dehydroxylation of kaolinite using thermogravimetric analysis and Controlled rate thermal analysis

The aim of this work was to identify parameters that could influence the conversion of kaolinite into metakaolinite. To this end, the dehydroxylation of four kaolinites, using controlled rate thermal analysis (CRTA) and thermogravimetric analysis (TGA), was investigated. X-ray diffraction (XRD) and Fourier transform infra-red (FTIR) were used to confirm the kaolinitic nature of the samples. Their crystallinity was evaluated using the Hinckley index from the XRD patterns and transmission electron microscopy (TEM) was used for morphological observation of the clay platelets. The thermal analyses of the samples indicate, for all samples, low defects as revealed by the low amount of adsorbed water on the clay surface. The dehydroxylation temperature from both techniques was influenced by the sample crystallinity and particle size. It was observed from both techniques that increase crystallinity resulted in highdehydroxylation temperature. Also, the influence of the clay platelets size on the dehydroxylation temperature, is proposed. All the results indicate that crystallinity and particle size are parameters that could be used to control the temperature for the conversion of kaolinite to metakaolinite.
 Keywords: Kaolinite; Crystallinity, Dehydroxylation; Thermal analysis

Controlled Rate Thermal Analysis (CRTA) as a Fast and Effective Method for the Development of Ceramic Powders of Synthetic Hydroxyapatite at Low Temperatures

One of the main limitations for applying synthetic hydroxyapatite as a filler in cement and other formulations in orthopedic surgery is its morphology. The present work shows the obtaining of synthetic hydroxyapatite powders at low temperatures such as 300 and 850ºC using the Controlled Rate Thermal Analysis (CRTA) technique. The powders obtained were characterized by IR spectroscopy and X-ray diffraction, showing that the phase formed corresponds to crystalline hydroxyapatite. The specific surface area values determined are between 17 and 66 m2/g with a pore size between 50-300 Å. The transformation of phases in the synthetic hydroxyapatite is studied by Dynamic Thermogravimetric Analysis and CRTA techniques, allowing the kinetic calculations of the transformation using two methods of data processing, determining the activation energy (Ea), pre-exponential factor (A), and model kinetic most likely in each stage. The results show the effectiveness and usefulness of the CRTA technique for preparing synthetic hydroxyapatite powders with different specific surface areas, which makes this technique attractive for medical purposes.

Synthesis, Crystal Structure and Thermal Decomposition of [HGdP2O7 · 2 H2O] · NH3 Electric properties of HGdP2O7 and Gd2P4O13

A new gadolinium diphosphate [HGdP2O7 · 2 H2O] · NH3 was synthesized via a soft chemistry route from evaporation of aqueous solution. It crystallizes in the space group Pī with Z = 2 and the following unit cell dimensions: a = 6.4609(2), b = 6.9810(2), c = 9.813(4) Ǻ, α = 81.345(3), β = 80.547(3), γ = 88.430(3)°. IR spectroscopy confirmed the presence of P-OH group, and both ammonia and water molecule in the studied material.The thermal decomposition of [HGdP2O7 · 2 H2O] · NH3, as investigated by Controlled Rate Thermal Analysis, took place in three stages between -23 and 600 °C leading to the anhydrous salt HGdP2O7. The calcination of the synthesized product at 850 °C in a static air furnace allowed us to obtain the tetraphosphate Gd2P4O13. X-ray powder diffraction and infrared spectroscopy were used to identify these materials.The electrical properties of HGdP2O7 and Gd2P4O13 were investigated through impedance complex analysis. Modest conductivity has been observed in both materials at relatively medium temperature range. Activation energies of 0.62 and 1.21 eV, were deduced from the Arrhenius plots for HGdP2O7 and Gd2P4O13, respectively.

Sample‐Controlled analysis under high pressure for accelerated process studies

AbstractThe potential of controlled rate thermal analysis (CRTA) for studying high‐pressure gas‐solid processes has been evaluated. CRTA is a type of smart temperature program based on a feedback system that uses any experimental signal related to the process evolution for commanding the temperature evolution. In this work, an instrument that uses the gravimetric signal for CRTA control has been designed and used for the study of two high‐pressure gas‐solid reactions: the highly exothermic thermal oxidation of TiC under high pressure of oxygen and the reduction in Fe2O3 under high pressure of hydrogen. Advantages of CRTA for discriminating overlapping processes and appraising kinetic reaction mechanisms are shown.

Study of the Biocompatibility and Corrosion Resistance of Hydroxyapatite Sol-Gel Thin Coatings on Ti6Al4V Alloy

The aim of this work was to prepare hydroxyapatite thin films (HAp) by a sol-gel method and to study the effect of thermal treatment temperature upon the biocompatibility and corrosion protection of these coatings on Ti6Al4V alloy. The HAp sol was obtained by hydrolysis and condensation of a mixture of triethyl phosphite and calcium nitrate tetrahydrate in stoichiometric amounts (i.e. maintaining a Ca/P ratio of 1.67) adapting a water-based route. The crystallite size and degree of crystallinity of the HAp sol-gel derived coatings strongly depends on the thermal treatment applied. Based on this knowledge, the HAp sol-gel films were annealing in air during 2h at 400ºC, 600ºC, 800ºC and 1200ºC, respectively. As an alternative to conventional thermal treatments, a set of samples was prepared by applying a modification of the Controlled Rate Thermal Analysis (CRTA) developed by Rouquerol, with the aim of obtaining HAp ceramic thin films with controlled textural characteristics at lower temperatures. The basis of this thermal treatment is to control temperature and pressure system, keeping constant the decomposition speed. The application of Thermogravimetric/Differential Thermal Analyses (TG/DTA) and X-ray Diffraction (XRD) has provided valuable information about the phase transformation, mass loss, identification of the phases developed, crystallite size and degree of crystallinity of the obtained HAp powders. Fourier Transformer Infrared Spectroscopy (FTIR) has been utilized for studying the functional groups within the prepared structures. The surface morphology and nature of the prepared HAp coatings was studied by Scanning Electron Microscopy (SEM) with energy dispersive spectroscopy (EDS). The specific surface (BET) and porosity of the material were determined starting from isotherms of adsorption for N2 at a temperature of 77 K. The corrosion protection behaviour of the HAp-coatings/Ti6Al4V in Kokubo’s Simulated Body Fluid (SBF) has been studied by Electrochemical Impedance Spectroscopy (EIS). Inductively Coupled Plasma (ICP) has been used to detect the concentration of Ca2+ and PO4 3- ions released and re-precipitated upon the HAp coatings submitted to soaking test in SBF. The quantification of the in vitro cytotoxicity of the HAp sol-gel coatings was made with human osteoblast cultures and a tetrazolium dye (MTT) based assay (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide)). Finally the analysis of the adhesion and cellular proliferation on the surface of the materials was also carried out. In these last studies Alamar Blue assays and human osteoblast cultures have been used. In summary hydroxyapatite nano-crystalline coatings on Ti6Al4V alloy have been obtained by a water-based sol-gel route. The crystallite size and degree of crystallinity of the HAp sol-gel derived coatings strongly depends on the thermal treatment applied. HAp films have been successfully obtained by annealing sol-gel-derived coatings in air during 2h at 600ºC and 800ºC. As an alternative to these conventional thermal treatments it has been possible to crystallize pure hydroxyapatite at 100°C of temperature of control for the pressure and 300°C as maximum temperature by applying controlled rate thermal analysis (CRTA) conditions. The obtained results have shown that the prepared coatings are nanocrystalline HAp with little deviations from that present in the human bone. All these HAp coating/Ti6Al4V systems have shown to have good bioactivity upon immersion in SBF, good biocompatibility and corrosion protection properties. Acknowledges The authors would also like to acknowledge the Ministerio de Economía y Competitividad of Spain (Projects MAT2012-38541-C02-02 and MAT2015-65445-C2-1-R) and Comunidad de Madrid (Project S2013/MIT-2862-MULTIMAT-CHALLENGE) for funding this research.

An insight on the weakening of the interlayer bonds in a Cameroonian kaolinite through DMSO intercalation

In this study, intercalation of dimethylsulphoxide (DMSO) in a Cameroonian kaolinite is used to achieve weakening of the interlayer hydrogen bonds, in the perspective of dispersion or even exfoliation of the clay within polymer composite materials. Displacement of intercalated DMSO by ethyl acetate and ammonium acetate is studied in order to simulate the interactions with the polymer matrix. The exfoliation of the kaolinite is well evidenced by X-ray diffraction and SEM observations. The disruption of the interlayer bonds is shown by the displacement of the FT-IR vibration modes of both Al–OH and Si–O functions, and by the decrease of the dehydroxylation temperature recorded by Controlled Rate Thermal Analysis. Complete displacement of DMSO by ethyl acetate is achieved and the crystalline structure is deeply disordered as a result of interlayer bonds weakening. The displacement of DMSO by ammonium acetate leads to a ternary composite of DMSO/ammonium acetate with respective intercalation ratio of 62.4% and 57.7%.

CO2 multicyclic capture of pretreated/doped CaO in the Ca-looping process. Theory and experiments

We study in this paper the conversion of CaO-based CO2 sorbents when subjected to repeated carbonation-calcination cycles with a focus on thermally pretreated/doped sorbents. Analytical equations are derived to describe the evolution of conversion with the cycle number from a unifying model based on the balance between surface area loss due to sintering in the looping-calcination stage and surface area regeneration as a consequence of solid-state diffusion during the looping-carbonation stage. Multicyclic CaO conversion is governed by the evolution of surface area loss/regeneration that strongly depends on the initial state of the pore skeleton. In the case of thermally pretreated sorbents, the initial pore skeleton is highly sintered and regeneration is relevant, whereas for nonpretreated sorbents the initial pore skeleton is soft and regeneration is negligible. Experimental results are obtained for sorbents subjected to a preheating controlled rate thermal analysis (CRTA) program. By applying this preheating program in a CO2 enriched atmosphere, CaO can be subjected to a rapid carbonation followed by a slow rate controlled decarbonation, which yields a highly sintered skeleton displaying a small conversion in the first cycle and self-reactivation in the next ones. Conversely, carbonation of the sorbent at a slow controlled rate enhances CO2 solid-state diffusion, which gives rise, after a quick decarbonation, to a highly porous skeleton. In this case, CaO conversion in the first cycle is very large but it decays abruptly in subsequent cycles. Data for CaO conversion retrieved from the literature and from further experimental measurements performed in our work are analyzed as influenced by a variety of experimental variables such as preheating temperature program, preheating exposition time, atmosphere composition, presence of additives, and carbonation-calcination conditions. Conversion data are well fitted by the proposed model equations, which are of help for a quantitative interpretation of the effect of experimental conditions on the multicyclic sorbent performance as a function of sintering/regeneration parameters inferred from the fittings and allow foreseeing the critical conditions to promote reactivation. The peculiar behavior of some pretreated sorbents, showing a maximum conversion in a small number of cycles, is explained in light of the model.

The Multistep Nature of the Kaolinite Dehydroxylation: Kinetics and Mechanism

The thermal dehydroxylation of kaolinite has been reexamined using small sample weights, a homogeneous particle size distribution and high‐vacuum conditions in order to reduce the influences of heat and mass‐transfer phenomena. The controlled rate thermal analysis (CRTA) technique, which was specially developed to minimize the pressure and temperature gradients through the sample, was employed to carry out meaningful kinetic experiments. Two advanced isoconversional methods, the Vyazovkin and the Galwey methods, were used complementarily to determine the dependence of the activation energy on the degree of conversion. For this purpose, the Vyazovkin method has been adapted to CRTA experiments. It was demonstrated that there are at least two different stages, revealing the multistep nature of this reaction. The activation energy for the first step, which is assigned to nucleation and the growth of nuclei, decreases from 100 to 75 kJ/mol. The second stage corresponds to a diffusion process and the activation energy rises to 120 kJ/mol because of the metakaolinite formation, which closes the interlamellar channels and leaves isolated patches of kaolinite from which the water escapes with difficulty.

Thermoanalytical studies of natural potassium, sodium and ammonium alunites

Dynamic and controlled rate thermal analysis (CRTA) has been used to characterise alunites of formula (M(Al)3(SO4)2(OH)6) where M ? is the cations K ? ,N a ? or NH4 ? . Thermal decomposition occurs in a series of steps: (a) dehydration, (b) well-defined dehydroxylation and (c) desulphation. CRTA offers a better resolution and a more detailed interpretation of water formation processes via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of water formation reveal the subtle nature of dehydration and dehydroxylation.

Kinetic Analysis of Inorganic Solid-State Reactions by Controlled Rate Thermal Analysis

Kinetic Analysis of Inorganic Solid-State Reactions by Controlled Rate Thermal Analysis

Temperature Control Modes in Thermal Analysis

Now we can use several temperature control modes, i.e., the isothermal run including stepwise heating and cooling, constant rate heating (or cooling), temperature control for sample thermal history, sample controlled thermal analysis (SCTA or controlled-rate thermal analysis, CRTA), temperature jump, rate jump, temperature modulation and repeated temperature scanning. Their advantages and drawbacks are reviewed with some illustrative examples, especially for application to kinetic analysis. The combined use of these varieties of temperature control mode is recommended by showing examples. Temperature modulation and repeated temperature scanning are discussed in comparison with temperature modulated DSC, and common and analogous points are elucidated. In relation to this, the possibility that an imaginary part of overall reaction rate constant in complex reaction is postulated. Finally,these modes are classified and tabulated from two viewpoints and other possible modes are shown.

Controlled rate thermal analysis of sepiolite

Controlled rate thermal analysis (CRTA) technology offers better resolution and a more detailed interpretation of the decomposition processes of a clay mineral such as sepiolite via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of non-isothermal nature reveal changes in the sepiolite as the sepiolite is converted to an anhydride. In the dynamic experiment two dehydration steps are observed over the ~20–170 and 170–350 °C temperature range. In the dynamic experiment three dehydroxylation steps are observed over the temperature ranges 201–337, 337–638 and 638–982 °C. The CRTA technology enables the separation of the thermal decomposition steps.

Thermoanalytical studies of silver and lead jarosites and their solid solutions

Dynamic and controlled rate thermal analysis has been used to characterise synthesised jarosites of formula [M(Fe)3(SO4)2(OH)6] where M is Pb, Ag or Pb–Ag mixtures. Thermal decomposition occurs in a series of steps. (a) dehydration, (b) well defined dehydroxylation and (c) desulphation. CRTA offers a better resolution and a more detailed interpretation of water formation processes via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of water formation reveal the subtle nature of dehydration and dehydroxylation. CRTA offers a better resolution and a more detailed interpretation of the decomposition processes via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of non-isothermal nature reveal separation of the dehydroxylation steps, since in these cases a higher energy (higher temperature) is needed to drive out gaseous decomposition products through a decreasing space at a constant, pre-set rate.

Dynamic and controlled rate thermal analysis of halotrichite

Three halotrichites namely halotrichite Fe 2? SO4� Al2(SO4)3� 22H2O, apjohnite Mn 2? SO4� Al2(SO4)3� 22H2O and dietrichite ZnSO4� Al2(SO4)3� 22H2O, were analysed by both dynamic, controlled rate thermogravi- metric and differential thermogravimetric analysis. Because of the time limitation in the controlled rate experiment of 900 min, two experiments were undertaken (a) from ambient to 430 C and (b) from 430 to 980 C. For halotrichite in the dynamic experiment mass losses due to dehydration were observed at 80, 102, 319 and 343 C. Three higher temperature mass losses occurred at 621, 750 and 805 C. In the controlled rate thermal analysis exper- iment two isothermal dehydration steps are observed at 82 and 97 C followed by a non-isothermal dehydration step at 328 C. For apjohnite in the dynamic experiment mass losses due to dehydration were observed at 99, 116, 256, 271 and 304 C. Two higher temperature mass losses occurred at 781 and 922 C. In the controlled rate thermal analysis experiment three isothermal dehydration steps are observed at 57, 77 and 183 C followed by a non-isother- mal dehydration step at 294 C. For dietrichite in the dynamic experiment mass losses due to dehydration were observed at 115, 173, 251, 276 and 342 C. One higher temperature mass loss occurred at 746 C. In the controlled rate thermal analysis experiment two isothermal dehydra- tion steps are observed at 78 and 102 C followed by three non-isothermal dehydration steps at 228, 243 and 323 C. In the CRTA experiment a long isothermal step at 636 C attributed to de-sulphation is observed.

Synthesis, characterization and thermal analysis of Fe-doped boehmite nanofibres and nanosheets

It is important that one should have knowledge of the thermal stability of synthesized nanomaterials. In this research, thermal analyses of both dynamic and controlled rate thermal analysis (CRTA) combined with infrared emission spectroscopy have been used to determine the thermal stability of iron-doped boehmite. Iron-doped boehmite nanofibres with varying iron contents have been prepared at low temperature using hydrothermal treatment in the presence of non-ionic poly (ethylene oxide) surfactant. The TEM images show that the resulting nanostructures are predominantly nanofibres when Fe doping is less than 5%; in contrast, nanosheets are the dominant for 10% Fe-doped boehmite. No nanofibre was observed in the case of 20% Fe-doped boehmite, instead, nanotubes, nanosheets and iron-rich nanoparticles were formed. Both dynamic thermal analysis and CRTA show that Fe-doped boehmite nanomaterials dehydroxylate at higher temperatures than pure boehmite nanofibres. In general, the higher the doped Fe %, the higher the dehydroxylation temperature. The dehydroxylation temperature indicated in the infrared emission spectroscopy of doped boehmite nanomaterials is in harmony with those in other thermal analysis studies.

Controlled rate thermal analysis of sepiolite

Controlled rate thermal analysis (CRTA) technology offers better resolution and a more detailed interpretation of the decomposition processes of a clay mineral such as sepiolite via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of non-isothermal nature reveal changes in the sepiolite as the sepiolite is converted to an anhydride. In the dynamic experiment two dehydration steps are observed over the ~20–170 and 170–350 °C temperature range. In the dynamic experiment three dehydroxylation steps are observed over the temperature ranges 201–337, 337–638 and 638–982 °C. The CRTA technology enables the separation of the thermal decomposition steps.

Surface analysis, TEM, dynamic and controlled rate thermal analysis, and infrared emission spectroscopy of gallium doped boehmite nanofibres and nanosheets

Ga doped boehmite nanofibres with varying Ga content have been prepared at low temperatures using hydrothermal treatment in the presence of poly (ethylene oxide) surfactant. The resulting nanofibres were characterized by X-ray diffraction (XRD), dynamic and controlled rate thermal analysis and infrared emission spectroscopy (IES), transmission electron microscopy (TEM), Energy dispersive X-ray analysis (EDX), N 2 adsorption/desorption. TEM results show that nanotubes are dominant when the doped gallium percentage is no more than 5%; nanosheets and an amorphous phase are observed in 10% and 20% gallium doped samples. N 2 adsorption/desorption analysis reveals a large amount of micropores and mesopores are present in the resultant samples. Similar to iron and yttrium doped boehmite nanomaterials, remarkable larger BET specific area was achieved compared to pure boehmite nanomaterials. Both dynamic and controlled thermal analyses show that the gallium doped boehmite nanomaterials dehydrate at higher temperature than that of pure boehmite. Interestingly, the higher the crystallinity of the resultant nanotubes is, the higher the dehydration temperature. The IES spectra show that dehydroxylation of the resultant gallium doped boehmite nanomaterials starts at 250 °C and is complete by 450 °C, in harmony with the dynamic and controlled rate thermal analysis results.

Thermal dehydration of CeP3O9·3H2O by controlled rate thermal analysis

The aim of this work is to highlight the importance of controlling the residual water vapour pressure above the sample as well as the rate of the thermal decomposition during the thermal dehydration of cerium cyclotriphosphate trihydrate CeP3O9·3H2O.

Chemical preparation and thermal behavior of neodymium cyclotriphosphate pentahydrate NdP 3O 9·5H 2O: A study by Controlled Rate Thermal Analysis (CRTA)

A new neodymium cyclotriphosphate pentahydrate powder, NdP 3O 9·5H 2O, has been prepared using a classical chemistry method and characterized by X-ray diffraction and infrared spectroscopy techniques. The IR spectrum shows the characteristic bands of cyclotriphosphates as the triplet in the range 1055–1007–917 cm −1. The thermal behavior of the titled compound was also carried out using conventional thermal analysis techniques (TG and DSC) under air atmosphere and Controlled transformation Rate Thermal Analysis (CRTA) technique under constant water vapour pressure of 5 hPa. It was shown that thermal treatment in air, with linear heating rate of 10 K min −1, favourites the structure breakdown as soon as the release of water molecules starts. In this case an amorphous compound is obtained, which then crystallizes at 1073 K and gives the polyphosphate Nd(PO 3) 3. However, by CRTA technique at P H 2 O = 5 hPa , the water molecules are eliminated with a lower rate which permits to save the initial structure up to an advanced dehydration step. The breakdown of the initial structure is immediately followed by the crystallization of the anhydrous polyphosphate Nd(PO 3) 3 phase in the temperature range 455 K < T < 793 K.

Thermal decomposition of hydrotalcite with hexacyanoferrate(II) and hexacyanoferrate(III) anions in the interlayer

The mechanism for the decomposition of hydrotalcite remains unsolved. Controlled rate thermal analysis enables this decomposition pathway to be explored. The thermal decomposition of hydrotalcites with hexacyanoferrate(II) and hexacyanoferrate(III) in the interlayer has been studied using controlled rate thermal analysis technology. X-ray diffraction shows the hydrotalcites have a d(003) spacing of 10.9 and 11.1 Å which compares with a d-spacing of 7.9 and 7.98 Å for the hydrotalcite with carbonate or sulphate in the interlayer. Calculations show dehydration with a total loss of 7 moles of water proving the formula of hexacyanoferrate(II) intercalated hydrotalcite is Mg6Al2(OH)16[Fe(CN)6]0.5·7H2O and 9.0 moles for the hexacyanoferrate(III) intercalated hydrotalcite with the formula of Mg6Al2(OH)16[Fe(CN)6]0.66·9H2O. CRTA technology indicates the partial collapse of the dehydrated mineral. Dehydroxylation combined with CN unit loss occurs in two isothermal stages at 377 and 390°C for the hexacyanoferrate(III) and in a single isothermal process at 374°C for the hexacyanoferrate(III) hydrotalcite.